Add local definition of sethostname to lxc_unshare
Add local definition of sethostname to lxc_unshare

sethostname doesn't exist on bionic, so copy/paste the definition of it
we have in conf.c

Signed-off-by: Stéphane Graber <089afc6d81f66f1168a9849e15660feae286e024@ubuntu.com>

ysbnim/lxc,DarknessBeforeDawn/lxc,fwilson42/lxc,federicobriata/lxc,akshaykarle/lxc,hallyn/lxc,codebauss/lxc,aeris/lxc,terceiro/lxc,Ponce/lxc,ss1h2a3tw/lxc,sapun/lxc,fwilson42/lxc,regit/lxc,LynxChaus/lxc,tych0/lxc,ioops/lxc,rowhit/lxc,szaszg/lxc,DarknessBeforeDawn/lxc,ioops/lxc,thmo/lxc,JohnPeacockMessageSystems/lxc,major/lxc,JohnPeacockMessageSystems/lxc,lazy404/lxc,lazy404/lxc,christiaan/lxc,tych0/lxc,sapun/lxc,terceiro/lxc,virajs/lxc,raspberrypython/lxc,ojkastl/lxc_Patches,Pelagicore/lxc,ksperis/lxc,major/lxc,LynxChaus/lxc,Distrotech/lxc,Pelagicore/lxc,yubo/lxc,caglar10ur/lxc,ojkastl/lxc_Patches,szaszg/lxc,hallyn/lxc,regit/lxc,virajs/lxc,lisongmin/lxc,thmo/lxc,aeris/lxc,yubo/lxc,caglar10ur/lxc,ysbnim/lxc,efiop/lxc,caglar10ur/lxc,federicobriata/lxc,regit/lxc,ksperis/lxc,cjwatson/lxc,weizhenwei/lxc,rldleblanc/lxc,ojkastl/lxc_Patches,weizhenwei/lxc,rldleblanc/lxc,cjwatson/lxc,bmoar/lxc,tych0/lxc,christiaan/lxc,GreatFruitOmsk/lxc,bmoar/lxc,bmoar/lxc,armcc/lxc,weizhenwei/lxc,Distrotech/lxc,codebauss/lxc,lazy404/lxc,ss1h2a3tw/lxc,szaszg/lxc,GreatFruitOmsk/lxc,Pelagicore/lxc,ecarrara/lxc,cjwatson/lxc,yubo/lxc,hallyn/lxc,rowhit/lxc,lisongmin/lxc,major/lxc,Distrotech/lxc,DarknessBeforeDawn/lxc,rldleblanc/lxc,akshaykarle/lxc,fwilson42/lxc,ysbnim/lxc,bostjan/lxc,hfuCN/lxc,thmo/lxc,JohnPeacockMessageSystems/lxc,armcc/lxc,ioops/lxc,bostjan/lxc,GreatFruitOmsk/lxc,Ponce/lxc,terceiro/lxc,QingweiPeterLan/cs188-lxc,jirislaby/lxc,hfuCN/lxc,ecarrara/lxc,akshaykarle/lxc,ojkastl/lxc_Patches,codebauss/lxc,armcc/lxc,hkjolhede/lxc,efiop/lxc,hkjolhede/lxc,rowhit/lxc,ecarrara/lxc,jirislaby/lxc,jirislaby/lxc,QingweiPeterLan/cs188-lxc,ss1h2a3tw/lxc,lisongmin/lxc,christiaan/lxc,bostjan/lxc,Ponce/lxc,federicobriata/lxc,sapun/lxc,QingweiPeterLan/cs188-lxc,aeris/lxc,ksperis/lxc,hkjolhede/lxc,raspberrypython/lxc,virajs/lxc,hfuCN/lxc,LynxChaus/lxc,efiop/lxc,raspberrypython/lxc